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i 35 methods of manufacturin Reiaaued Aug. 23, 1927.

UNITED STATES Re. 16,709 PATENT OFFICE.

ANDB LEW I. FAIRLIE, OF ATLANTA, GEORGIA,

nxoovmnr or oxmnsor mrnoeniv m SULPEUBIC-ACID universe-rune.

2N0 Drawing, lo. 1,420,477, dated June .20, 1922, Serial No. 382,519 filed Kay 19, 195 30.

Application for reissue fled August 24, 1926. Serial No. 131,805.

' In the manufacture of sulphuric acid by the so-called chamber process, and also by some of the so-called tower processes, it is usual to treat gases containing sulphur di- 5 oxide and oxygen (or air) with oxides of nitrogen, this treatment being efiected in the presence of .moisture, the moisture being either in the form of steam orv water vapor or in the form-of a spray of liquid water or dilute acid containing water, or sometimes.

the water'may be supplied in other ways. At the end of the acid-making apparatus a vvery large percentage of the nitrogen compounds introduced into-the beginning of the acid making. system exists in the gases in the formof oxides of nitrogen and these oxides can be'referred'to as the higher oxides and the .lower oxides of nitrogen.

The usual custom in the chamber process is to pass the gases leaving the last lead chamher through a tower commonly called a Gay- Lussactower, in which the gases are treated with cool and moderately concentrated sulpiiuric acid, the concentration of the aciding such that it will absorb from the gases the majorpart at least ofvthe ox des of nitrogen present the gases. However, the absorption"of nitrogen compounds in the Gay-Lussac tower as ordinarily operated, 1S

' not complete, and the gases leaving this tower may containa substantial quantity of oxides of nitrogen. v

In, my 'reviously issued Patent No. 1,205,723, escribingan improvement in sulphuric acid, I stated that nitrogen oxi es escaping from the last lead chamber of a sulphuric acid plant are most advent "eously absorbed in the Gay-Lussac tower w en a small percent- 40 age of sulphur dioxide (usually not less than .0570 nor more than ..15% by volume) is present in the as mixture. Further exrience of myse f and others serves to conrm the truth of this statement,

, In attempting to absorb in water the ni-' trogen oxides'escaping absorption in the sul phuric acid in the Gay-Lussac tower, I discovered that these residual nitro en oxides were not readily nor completely absorbed in water. I ascertained that-this failure to be readily absorbed by water was due to the presence in the gas mixture of the small quantity of sulphur dioxide referred to a above, which kepta' substantial part of the 95 residual nitrogen oxides reduced to the lower or oxygen can be introduced, if needed.

state of oxidation. If a Gay-Lussac tower be used for the absorption of the nitrogen oxides, the resence of the small ercentage of sulphur ioxide referred to is highly desirable. If a water absorption of residual 00. oxides of nitrogen is to follow the Gay-Lus-- sac tower absorption, these traces of sulphur dioxide are big 1y undesirable during such water absorption. v

In accordance with the present invention, I aim to remove the total quantity of sulphur dioxide from the gases, whereby the oxides of nitrogen can readily combine with oxygen of the air present (or with oxy en in-. troduced into the gases, either as suc or in the form of air) whereby higher oxides of nitro en will be formed and subsequently I absor as completely as possible, -these higher'oxides of nitrogen; Ordinarily, the gases leaving the latter part of the acidmaking plant will contain ample free oxygen for the complete oxidation of the SO, and lower oxides of nitrogen, but as stated, air

, Several difierent methods may be employed for the complete removal of the sulphur dioxide present in the ases, and for the purpose of illustration I give below four dilferent methods by which such operation can be conveniently efl'ected.

In the first modification, the gases from the Gay-Lussac tower of an acid plant, 1or example of the chamber type, are led through one or more towers lIl WhlCl'l the said gases are treated with lime, this preferabl being hydrated lime, and either the. dry ydrate or milk of lime or even lime water may be employed, but milk of lime is ordinarily to be preferred. Since the major part of the oxides of. nitrogen present in the gases leaving the Gray-Lussac tower, are in the form of the lower oxides, milk of lime will not, under ordinary conditions, absorb or unite with any very considerable portion of these oxides, but the milk of lime will readily and I or other absorbing medium. The passage of the gas through such latter absorption apparatus may conveniently be effected rather slowl in order to permitthe lower oxides of nitrogen to become substantially completely oxidized to the higher oxides of nitrogen which latter are readil absorbable in water with the production 0 nitric acid.

In order to revent as much as possible,.

oxidation of t e lower oxides of nitrogen to the higher oxides in the lime treatin towers oiabsorbers, it is advisable to pass the gases through the lime apparatus at a. rather rapid rate, since it is not desired toabsorb any substantial quantities of theloxides of nitrogen by the lime.

In the second of the processes mentioned by way of example as illustrative of the present invention, I may pass the gases leaving the Gay-Lussac tower, with or without the addition of, free oxygen (e. g., air) through an apparatus for the catalytic oxidation of SO to S0,. Preliminary to this operation the gases are preferably heated up considerably, which ma be done in large part by.a suitable interc anger, afterwhich the gases are passed over or through a suitable catalyzer material, as in the contact process of making sulphuric acid, and there-- after the heat of the gases leaving the catalyzer is imparted to the cooler entering gases: The S0, formed in this operation may be suitably removed, for example-by or gaseousform in appropriate apparatus according to this" nature of the oxidizing agent employed.

condensation after adding steam or water or liquid sul huric acid. The gases'may then be a'sse through appropriate apparatus for urther cooling and oxidation, and

. are then passed into and through the nitrogen oxide absorbers, as above referred to.

The third modificationof this invention is similar to the second, except that instead of completely oxidizing the sulphur dioxide by a catalytic process the completeoxidation of the sulphur dioxide is efiected by treatment with a chemical oxidizingagent, such was bromine,. iodine, chlorine, bleach ing powder, sodium or, hydrogen peroxide, a

- erman anate, a ferric or ot or highly oxiized sa t, or the like, in either solid, i

quid

As a fourth form of execution of the presentiinvention, the gases, from the lastlead.

chamber-ma be used without previous treatment in a sired) be admitted into t e gases entering j this masonry chamber. The size of the v ay-Lussac tower. In this forin of o eration, the are passed from the masonry chamber will vary considerably, from 1 to 25% of the total lead chamber space may be needed and in most cases between 5 and 15% of the total lead chamber space will be found to be a suflicient size for the masonry chamber. Inthis masonry chamber the entire amount of SO present in the gases will be converted into sulphuric acid and substantially the entire quantity of lower oxides of nitrogen resent in'the gases w1ll be converted into lug er oxides of mtrochamber above referred tobeing made of material which is resistant to both nitric and sulphuric acids, the excess of higher oxides of nitrogen in the gases can do no harm. The sulphuric acid formed may be condensed, or it may proceed as mist into the absorbing apparatus.

" For a single masonry chamber, or other 7 type of chamber, resistant to nitric acid, a series or group of such chambers may be substituted, for the complete oxidation of.

the sulphur dioxide and the lower oxides of nitrogen. Sinc'e.the oxidation of thelow'er absorption in strong sulphuric acid, or by oxides of nitrogen goes on more rapidly 1f the gas mixture is cool. it is usuall preferable to intermingle oxidation cham rs with cooling devices or ap aratus, whereby the gases may be cooled by means of flowing water (usually iniindirect contact), or in the gases maytravel to a-suitable apparatus for the absorption 'of the higher oxides of nitrogen for example the water absorbers above referred 'to. 4

It will thus :be seen that in'the various modifications of myprocess forming the subject matter of the present application, I first treat the exit gases of any system in which sulphuric acid is manufactured by the employment of oxides of nitrogen, to remove from such gases as completely as possible, the sulphur dioxide present-therein and I recover the sulphuric acid formed, and Ifallow and induce the conversion of the loweroxides of'nitrogenpresent as completely as. possible into the higher oxides, of nitrogen, coolin the ases to facilitate this conversion, if esired: and I. absorb the A suitable tower for main t e process is acidenaking system. omitted if'deeired, and the nitrogen comthat described in my co-pending application filed April 21, 1920.,

In this latter operation, a bi h efiiciency can be secured, since substantia y all of the nitrogen is in the form of the higher oxides.

If desired, the escaping from the watertreatment may be Sub ected to a lime or alkaline treatment, to more completely recover the ni n oxides. In some instances. it might" advisable, in place of employing apparatus in which the oxides of nitrogen are absorbed in water, to emplo an ordinary Gay-Lussac tower fed wit sulphuric acid of the strength adapted for absorption of the oxides of nitrogen, or some other suitable absorbing medium may be employed.

The nitric acid or nitrosulphuric acid, or other nitrogencompound, produced by the absorption of the oxides of nitrogen by any of the modifications of the methods herein described can be utilized, for example by feeding to'the Glover-tower or towers, or b otherwise introducing into the sulphuric acid-making system.

"The invention herein described'comprises, then, the following steps, as ap lied (A? to. Gay-Lussac exit gases, and B) to ead chamber exit ases:

1. Substantially com lete elimination from the gas mixture 0' traces of sulphur dioxide, either by- (0; Absorption in lime water or alkali. (b Oxidation b' catalytic agent. (a) Oxidation y chemical oxidizing agent.

(d) Oxidation by 'air or oxygen, as in modification 4.

2. Hydration of the sulphur trioxide and preci itation as sulphuric acid if desired. 3. the gas mixture, if desired. 4. Oxidationof lower oxides of nitro en to higher oxides, with or without the dition of oxy 'ea or air. (Steps 3 and 4 may be cgritinue aiternately as frequently as desire 5. Absorption of oxides of nitrogen, preferably in. water.

it. Utilization of the recovered oxides of nitrogen by returning same to the sulphuric (This step may be pounds used or disposed. of otherwise.)

The principal advantages which this invention ofiers over the'priorart are:.

- A higher yield oi sulphuric acid. The

amount of sulphur dioxide escaping from the Gay-Jimmie tower amounts to at least one per cent, and in many cases to two or inc meal equivalent.

three r cent, or more, of the total sulphur dioxi e admitted to the Glover tower. All of this escaping sul hur dioxide is by several modifications o my method, recovered as liquid sulphuric acid; e

2. A higher percentage of recovery of nitrogen oxides, resulting in a substantial economy in operating expenses for sulphuric acid manufacture.

3. Modification 4, in which the sulphuric acid-fed Gay-Lussac tower may be eliminated may also eliminate the disadvantages of circulating a large quantity of-sulphuric acid over Gay-Lussac and Glover towers, whichinclude: (a) Impeded draft, due to sediment de- 'ted by the circulating sulphuric acid in the interstices of the tower packing, resulting in waste of war for moving the ases in impaired el ienc of the plugged ay-luussac tower. as an a orber of nitrogen oxides, and in waste of sulphur dioxide.

(b) Waste of labor, water, sulphuric acid,

and oxides of nitrogen, while washing sedi ment out of a plugged tower.

(c) Expense of cooling a large quantity of sulphuric acid (usually two or three times the daily capacity of. the plant) for use on the Ga -Lussac tower.

s of sulphuric acid as spray or tower.

I have referred above to washing gases containing higher oxides .of nitrogen with water, say in towers or like devices. It will be obvious that when water (even pure water) is first brought in contact with gases containing higher oxides of nitrogen, the latter are (in part atleast) absorbed by such water form nitric acid, so that the actual washin liquid in said operations will be, when t e same has traveled, downwardl even a short distance in contact with 5001 gases, a mixture of water containing more or less nitric acid. Hence where I refer to washing the gases with water, this obviously includes was ing the gases with water containing more or less nitric acid, or in other words, a. more or less dilute nitric acid.

I have above referred to treating (A). exit gases from a Gay-Lussac tower; or

exit gases from lead chambers or their tower the ases are washed with cool. sulhuric aci These gases may thereafter treated with water (aqueous liguid}. Hence in this case there may be a succession of absorptions, i. a, first with acid in a Gay- Lussac tower, then. with aqueous liquid. This latter will form liquid containing nitric acid. the exit gem from a Gay- Lussac tower may he treated with chemical oxidising agent. for the removal or oxidation of the last, traces of sulphur dioxide from said and thereafiter the E In the Gay-Lussac gases may be treated with water or aqueous liquid forjthe absorption of the higher oxides of nitrogen, the lower oxides of nitrogen being rapidly oxidized to higher oxides after the removal of the sulphur dioxide In this case there may be a succession of steps as follows: first, absorption ofnitrogen oxides in sulphuric acid in a Gay-Lussac tower; second, oxidation of residual sulphur dioxide by means of a chemical oxidizing'agent; third, absorption of oxides of nitrogen in an aueous liquid. Or, the exit gases from a ay-Lussac. tower may. be treated with a chemical oxidizing agent, -a's aforesaid, for the complete removal of sulphur dioxide from the gases, and thereafter the.'said gases may be again treatedwith water or sulphuric acid for the absorption of higher oxides of nitrogen, as indicated above. In this latter case, the succession of steps would be: first, absorption of nitrogen -oxides in a Gay-Lussac tower; second, oxidation of residual sulphur dioxide by means of a chemical oxidizing agent; third, absorption of oxides of nitrogen in water, or in sulphuric acid.

l When the gases to be treated are ases discharged directly from the lead cham rs,

the sulphur dioxide in "such gases may be oxidize by means of a'chemical oxidizing a cut, e. g., air and nitrogen oxides, in

w ich operation some water also ma be present, for the complete removal 0 the sulphur dioxide, and thereafter the nitrogen oxides may be absorbed in water, the succession of ste s being: first, oxidation of sulphur dioxi e by agency of an oxldized compound of nitrogen; second, absorption of nitrogen oxides 1n water. Or, after the oxidation of sulphur dioxide as aforesaid, the absorption of nitrogen oxides may take place in sulphuric acid as indicated above,

the succession of steps being: first, comp'lete removal ofjsulphur dioxide by means ofan oxidized compound of nitrogen; second, absorption of oxides of nitrogen in sulphuric acid.- Thus, there are-several sequences of .water and sulphuric [acid de- "troducingl, air or scribed. Obviously, should any small amounts of sulphur dioxide be present in the gases at the time of treatment of the' said gases with water containing nitric acid,

the' said acid would promptly oxidize the sul hur dioxide. v

- have referred to the possibilit of ino gen, etc., into t egases after wit drawing rom the last chamber or G'ay-Lussac tower. Ordinarily the gases already will containsufiicient oxygen for thepurpose. Y I v I claim a 1. A process of recovering the nitrogen oxides present in the exit gases discharged from a sulphuric acid manufacturin plant, which consists in first substanti y comnitrogen in water.

steps of first substantiall pletely removing the sul hur dioxide from such gases, thereafter oxi izing the oxides of nitrogen to the higher stateof oxidation and absorbing the same. 5

' 2. A process of recovering the nitrogen oxides present in the exit gases of sul huric acid manufacture-which comprises su stantially completely oxidizing the sulphur dioxide content thereof and thelower' oxides of nitrogen, and absorbing the oxides of 3. A process of recovering the nitro en oxides present the gases leaving the ast lead chamber. (or its technical equivalent) of a sulphuric acid manufacturing plant employing a nitration process, which consists in passing such gases into a structure resistant to the action of nitric acid, allowing .or causing therein the substantially complete ox'idation of the sulphur dioxide, and allowing or causing the oxidation of thebulk of the.

lower oxides of nitrogen into-the hi' he oxides to take place, and thereafter absorbing the latter.

4. lhe process of removing from the exitgases of a sulphuric acid manufacturing plant, the normal content of sulphur dioxide therein, oxidizing the lower oxides of nitrogen to h gher oxides, and absorbing the latter- I' 5. A process of recovering the oxides of nitrogen present in the gases leaving a su1- phuric acid-making a paratus employing oxides of nitrogen, whic consist in substantially completely removingthe sulphur dioxidefrom such gases, thereafter cooling the remaining gases containing the oxidesof nitrogen while in contact with a substantial excess offree ox gen, whereby the lower oxides are oxidize to the higher oxides, and

finally absorbing the latter.

6. A process of treating the gases leaving an apparatus for the manufacture "of sulphuric acid involving the useofoxides of nitrogen, which comprises, first, substantially completely removing the sulphur di-" oxide. from such gases by oxidizing and bydrating the same to produce an additional quantity. of sulphuric acid, then oxidizing substantially the entire amount of the lower oxides ofnitro en present in the gases into the higher oxides, and finally absorbing the said higher ox des of nitro en.

7. In the manufacture o sulphuric acid by the lead-chamber process, a. process of recovering nitrogen oxides comprising the complete y moving the sulphur dioxi e from the if? at a'late sta e of the sulphuric acid ma g process, oxi izing the lower-oxides of nitrocovering nitrogen oxides from the gas mix- 125 gen, and absorbing the higher oxides of comprises first substantiall present in such gases, then oxidizin turedischarged from thelast chamber, which completely removing the sulphur dioxi e from the gas Vmixture after leaving the last chamber, then ing plant, which comprises first substantially completely removing the sulphur dioxige t e ower oxides of nitrogen present to hlgher oxides, then absorbing the higher oxides of nitrogen, and then returning the absorbed nitrogen-o gen compounds to such sulphuric aci plant for use in the manufacture of sulphuric acid.

10. An improvement in the process of making sulphuric acid by methods involvingthe use of compounds containing nitrogen and oxygen, which comprises withdrawing from the latter part of the plant in which such process is conducted, gases containing not more than a small percentage of 80,, substantially completely oxidizing any SO in said gases and thereafter oxidizing lower oxides of nitrogen in said gases and thereafter absorbing the higher oxides of nitrogen from said gases by contact with a liquid, and introducing liquid carrying such absorbed oxides of nitrogen into a Glover tower used in a sulphuric acid producing operation.

11. An improvement in the process of making sulphuric acid by methods involving the use of compounds containing nitro en and oxygen, which comprises withdrawing from the latter part of the plant in which such process is conducted, gases containing a small percentage only of 80,, substantially completely oxidizing such S0 and there-- aftsr oxidizing lower oxides of nitrogen in em higher oxides of nitrogen from said gases by contact with an aqueous liquid, and in troducing liquid carrying such absorbed oxides of nitrogen into the Glover tower of the acid-making plant.

12. A process of recovering the nitrogen oxides present in the exit gases discharged from the sulphuric acid manufacturing plant, which consists in first substantially completely removing the sulphur dioxide from such gases, thereafter oxidizing the 1 oxides of nitrogen to a higher state of oxidation and absorbing the same, and introducing resultant product of said absorption step, into the Glover tower.

13. A process of recovering the nitrogen oxides present in the exit gases containing some-SO discharged from a sulphuric acid manufacturing plant, which consists in first gases and thereafter absorbing thesubstantially completely-h removing the phur dioxide from such gases, thereafter oxidizing the oxides of nitrogen to the higher state of oxidation and absorbing the same in liquids, including a liquid consisting largely at least. of water as one of the absorbents, to form nitric acid, and intrm ducing the nitric acid so formed into the Glover tower.

14. -A process of recovering the nitrogen oxides present in the exit gases of sul huric acidmanufacture which comprises su tantially completely oxidizing the sulphur dioxide content thereof and the lower-oxides of nitrogen, and absorbing the oxides of nitrogen in water to form nitric acid, and

15. A process of recovering the nitro en oxides present in the gases leaving the ast lead chamber (or its technical equivalent) of a sulphuric acid manufacturing plant employing a nitration process, which consists in passing such gases into a structure resistant to the action of nitric acid, allowing or causing therein the substantiall complete oxidation of .the sulphur dioxi e, and allowing or causing the oxidation of the bulk of the lower oxides of nitrogen into the higher oxides to take place, and thereafter absorbing the latter in an aqueous liquid to form an acid liquid containing nitric acid and introducing same into a Glover tower.

v 16. A process of recovering the nitrogen oxides present in the gases leaving the last lead chamber (or its technical of a sulphuric acid manufacturing plant employing oxygen compounds of nitrogen, which consists in passing such gases into a structure resistant to the action of nitric acid, allowing or causing the substantially complete oxidation of any sulphur dioxide uivalent) contained in said gasesand allowing or causing therein the oxidation of the bulk of the lower oxides of nitrogen into the higher oxides to take place, and thereafter absorbing the latter in a succession of liquid treatments and introducing the liquid product containing such absorbed nitrogen oxides ter in a series of liquid absorbing agents,v

one of said liquids being essentially water, and feeding the liquid resulting from such water treatment into a Glover tower. v y

18. A process of recovering the'oxides of nitrogen present in the gases leaving a sulphuric acid-making apparatus employing oxides of nitrogen, which consists in substantially completely removing the sulphur dioxide from such thereafter cooling 19. A process of treating the gases leaving an apparatus for the manufacture of sulphuric acid involving the use of oxides of nitrogen, which comprises, first, substantially completely removing the sulphur dioxide from such gases by oxidizing and hydrating the same to produce an additional quantity of sulphuric acid, then oxidizing substantially the entire amount of the lower oxides of nitrogen present in the gases into the higher oxides, and finally absorbing: the said higher oxides. of nitrogen and contacting the absorbent carrying the so-absorbed oxides of nitrogen with the hot gases containing SO in an early stage ofthe acid making process.

20. Aprocess of treating the gases leaving an apparatus for the manufacture of sulphuric acid involving the use of oxides of nitrogen, which comprises, first, substantially completely removing the sulphur di-v oxide from such gases by oxidizing and hydrating the same to produce an additional quantity of sulphuric acid, then oxidizing substantially the entire amount of the lower oxides of nitrogen present in the gases into the higher oxides, and finally absorbing the said higher oxides of nitrogen and contacting the absorbent carrying the so-absorbed oxides of nitrogen with hot gases containing SO, in a Glover tower.

21. A process which comprises subjecting the exit gases discharged from a sulphuric acid making plant to treatmentwitha chem- I ical oxidizing agent to oxidize any residu il sulphur dioxide therein, and thereafter oxidicing the low oxide of nitrogen therein into a higher state of oxidation, and absorbing such higher oxide of nitrogen from said gases and introducing the resulting liquid into a Glover tower. s

22. In the manufacture of sulphuric ac'1d by the use of nitrogen-oxygen compounds,

H16 herein described process which comprises passing, gases from the latter pmt' of the sulphuric acid making system, while in con tact with some free oxygen, into contact with water, until such water contains a substantial percentage of nitric acid, and thereafter introducing such nitric acid into the Glover tower of a sulphuric acid making plant, whereby its content of nitrogen-- oxygen compounds is reintroduced into the sulphuric acid making system.

23. In the manufacture of sulphuric acid by a method involving the use of compounds containing nitrogen and oxygen, the herein described steps of withdrawing the I exit gases from a part of a sulphuric acid making plant near the rear end thereof, into a structure of which a part at least is resistant to action of nitric acid maintaining therein conditions favorable to oxidation of constituents thereof, and continuing suchiconditions until a large part at least ofthe lower oxides of nitrogen have been oxidized to higher oxides of nitrogen, and subjecting such gases to the action of a liquid absorbent capable of absorbing higher oxides of nitrogen, and thereafter introducing such acid making plant.

24. In the manufacture of sulphuric acid a by a method involving the use of compounds containing nitrogen and oxygen, the herein described steps of withdrawing the exit such gasrs to the action of an aqueous liquid 'to absorb higher oxides of nitro' en, and

thereafter introducing such liqui, into a Gilover tower of a sulphuric acid making p ant. V j

'25. A process of recovering the nitrogen oxides present in the gases leaving the last lead chamber (or its technical of a sulphuric. acid manufacturing plant employing a. nitration process, which consists in passing such. gases into a structure resistant to the action of nitric acid, allowing or causing therein the substantially complete oxidation of any sulphur dioxide contained therein, and allowing or causing the oxidation of the bulk of the lower oxides of nitrogen into the hi her oxides to take place, and thereafter a sorbing the latter in an uiva'lent) absorbent liquid andintroducing the product containing such absorbed nitrogen oxides into a Glover tower.

26. In a process of manufacturing sulphurieacid y means of a. nitrogen-oxygen compound, the process of recovermg the nitrogen oxides present in the chamber gas mixture which comprises substantially completely oxidizing the sulphur dioxide. .contained in thegases of the rear part of the sulphuric acid making part ofthe acid plant,-

- and also oxidizing lower oxides of nitro in said gases to higher oxides, and absorbmg the latter, and introducing the liquid'containing the absorbed oxides of nitrogen into the Glover tower.

27. In the chamber process for the manufacture of sulphuric acid, the process of reliquid into a Glover tower of a sulphuric i covering oxides of nitrogen from the gas mixture leaving the lead chambers, which comprises continuously permitting the substantially complete oxidation. of S0 in the gases, cooling the remaining gases, oxidizing the lower oxides of nitrogen to higher oxides. and absorbing at least part of the latter in a. liquid initially consisting essentially of water for the production of nitric acid, and passing the nitric acid so produced to a Glover tower for use in the production of sulphuric acid.

28. In the chamber process for the manufacture of sulphuric acid. the processof recovering nitrogen oxides from a gas mixture containing the same but containing no S0 and coming from a sulphuric acid'making process, which comprises allowing and inducing the conversion of lower oxides of nitrogen to higher oxides of nitrogen, cooling the gas mixture. and absorbing at least part of the higher oxides of nitrogen in water to form nitric acid and feeding the liquid containing such nitric acid to a Glover tower.

29. In the chamber process for the manufacture of sulphuric acid. theprocess of re covering nitrogen oxides from a gas mixture containing the same leaving the sulphuric acid making part, of a sulphuric acid plant. comprising first treating such gas mixture to oxidize substantially completely the SO present therein. thereby producingan additional quantity of sulphuric acid. and allowing and inducing the conversion of lower oxides of nitrogen to higher oxides and absorbing at least part of the higher oxides of nitrogen in a liquid adapted for the absorption of higher oxides of nitrogen.

30. In the manufacture of sulphuric acid by the chamber process the process of recovering nitrogen oxides which comprises first nitrogen to higher oxides of nitrogen, and

thereafter absorbing at least part of the higher oxides in a liquid.

31. In the manufacture of sulphuric acid by the use of oxides of nitrogen. the herein described process which comprises cooling -thc gases after leaving the latter part of'a sulphuric acid-making plant and passing said gases into contact with water, until such water contains a substantial percentage of nitric acid. and thereafter introducing such nitric acid into the Glover tower of a sulphuric acid plant.

32. In the manufacture of sulphuric acid by the chamber process, the process of recovering nitrogen oxides from the gas mixture containing the same and also some'free oxygen, such gases coming from the rear part of a sulphuric acid-making apparatus, comprising the steps of cooling such gas mixture. permitting oxidation of lower oxides of nitrogen contained therein into higher oxides of nitrogen. contacting such gas mixture with an aqueous liquid to produce a liquid nitric acid. and introducing such liquid containing nitric acid into a Glover tower.

In the process of manufacturing sul phuric acid by means of a nitrogen-oxygen compound,-the process of recovering the nitrogen oxides in the gas mixture dischm'gcd from the last lead chamber or its technical equivalent, which comprises cooling such gas mixture and treating such gas mixture with a chemical oxidizing agent and with an absorbent liquid for oxides of nitrogen.

ANDREW M.- FAIRLIE. 

